Q: What happens if I want to use my original Xbox console after I've started using my new Xbox 360 console? Can I still fire up an old favorite and jump online?

A: You sure can. No matter which system you were using when you started your Xbox Live membership, you can sign in to Xbox Live from either console as long as you maintain the same gamertag and keep your membership paid up.

http://www.xbox.com/en-US/support/sy...grationfaq.htm